1. Field of the Invention
The present invention relates to a dielectric element and a method of manufacturing the same, and more specifically, it relates to a dielectric element such as a capacitor element employing an oxide dielectric film and a method of manufacturing the same.
2. Description of the Prior Art
A ferroelectric memory is recently energetically studied as a high-speed nonvolatile memory requiring low power consumption. An oxide ferroelectric substance having a bismuth layer structure such as SrBixTa2O9 (SBT) or an oxide ferroelectric substance having a perovskite structure such as PbZr2Ti1xe2x88x92xO3 (PZT) is employed as a ferroelectric material for such a memory. Also in relation to a dynamic random access memory (DRAM), employment of a high dielectric material having a higher dielectric constant than a silicon oxide film or a silicon nitride film is studied following increase of storage capacity resulting from higher densification and higher integration of a memory element. An oxide dielectric film of SrTiO3 (STO), Ta2O5 or BaxSr1xe2x88x92xTiO3 (BST) is employed as the high dielectric material.
In a memory employing the aforementioned oxide dielectric film as a capacitor insulator film, a capacitor element is generally covered with an interlayer dielectric film such as an SiO2 film or an SiN film after formation thereof.
In the process of forming such an interlayer dielectric film, however, hydrogen gas generated as a reaction product disadvantageously reduces the oxide dielectric film. Therefore, ferroelectric characteristics are deteriorated and the dielectric constant of the capacitor is reduced.
A semiconductor memory employing a MOS (metal-oxide-semiconductor) transistor as a switching transistor requires a step of recovering a lattice defect caused in a manufacturing step with gas containing hydrogen. Also in this case, ferroelectric characteristics are deteriorated and the dielectric constant of the capacitor is reduced due to hydrogen gas similarly to the above. Particularly when an electrode of the capacitor is prepared from Pt or Ir, characteristic deterioration is remarkably caused due to the catalytic action thereof.
An object of the present invention is to provide a dielectric element having excellent characteristics by suppressing diffusion of hydrogen.
Another object of the present invention is to provide a method of manufacturing a dielectric element capable of readily manufacturing a dielectric element having excellent characteristics by suppressing diffusion of hydrogen.
A dielectric element according to a first aspect of the present invention comprises a lower electrode including a first conductor film containing a metal, silicon and nitrogen, a first insulator film including an oxide dielectric film and an upper electrode including a second conductor film containing the metal, silicon and nitrogen, while the metal includes at least one metal selected from a group consisting of Ir, Pt, Ru, Re, Ni, Co and Mo.
In the dielectric element according to the first aspect, the first and second conductor films function as barrier films preventing diffusion of hydrogen in the aforementioned structure. The aforementioned metal (M) hardly forms a nitride in general or is stabilized as MxN (xxe2x89xa72) when forming a nitride. When bonded with silicon (Si) and nitrogen (N), the metal (M) is more readily bonded to Si than to N, while N is readily bonded to Si. Therefore, the M-Sixe2x80x94N film is conceivably in a structure having Sixe2x80x94N embedded in metal silicide (M-Si). Thus, the M-Sixe2x80x94N film can conceivably have a hydrogen diffusion preventing function of the silicon nitride film (Sixe2x80x94N) and conductivity of the metal silicide film (M-Si) at the same time. Consequently, the first and second conductor films can prevent hydrogen from diffusing into the oxide dielectric film. Thus, the oxide dielectric film can be prevented from deterioration of characteristics.
In the dielectric element according to the aforementioned first aspect, the first insulator film including the oxide dielectric film is preferably enclosed with the lower electrode including the first conductor film, the upper electrode including the second conductor film and a second insulator film having low permeability for hydrogen. According to this structure, an end of the oxide dielectric film not covered with the first and second conductor films is also enclosed with the second insulator film having low permeability for hydrogen, whereby hydrogen can be further suppressed from diffusing into the oxide dielectric film. In this case, the second insulator film having low permeability for hydrogen is preferably removed in a region other than an element region formed with the first insulator film, the lower electrode and the upper electrode. According to this structure, hydrogen can be suppressed from infiltrating into the element region including the oxide dielectric film while a step of recovering a MOS transistor with hydrogen can be unlimitedly carried out in the region other than the aforementioned element region.
In the dielectric element including the aforementioned second insulator film, the second insulator film having low permeability for hydrogen preferably includes at least any of a silicon nitride film, a silicon oxynitride film and an aluminum oxide film. According to this structure, hydrogen can be effectively suppressed from infiltrating into the oxide dielectric film.
In the dielectric element according to the aforementioned first aspect, the first insulator film including the oxide dielectric film is preferably formed to cover the upper surface and the side surface of the lower electrode, while the upper electrode is preferably formed to cover the upper surface and the side surface of the first insulator film. According to this structure, the side surface of the first insulator film including the oxide dielectric film is not exposed sideward, whereby hydrogen can be prevented from directly infiltrating into the oxide dielectric film or the interfaces between the oxide dielectric film and the lower and upper electrodes.
In the dielectric element according to the aforementioned first aspect, the first conductor film is preferably formed on a plug. According to this structure, a stacked capacitor structure capable of preventing hydrogen from diffusing into the oxide dielectric film can be readily formed, for example. In this case, the plug preferably includes either a polysilicon plug or a tungsten plug. According to this structure, a generally employed technique of forming a polysilicon plug or a tungsten plug can be applied as such.
In the dielectric element according to the aforementioned first aspect, the lower electrode may include the first conductor film consisting of an IrSiN film and a Pt film formed on the first conductor film. The upper electrode may include the second conductor film consisting of an IrSiN film and a Pt film formed on the second conductor film. Further, the upper electrode may include a Pt film and the second conductor film, formed on the Pt film, consisting of an IrSiN film. In addition, the first insulator film including the oxide dielectric film may include an SBT film.
A method of manufacturing a dielectric element according to a second aspect of the present invention comprises steps of forming an interlayer dielectric film having an opening reaching a conductive region on a semiconductor substrate including the conductive region, forming a plug in the opening by forming a conductive material in the opening and on the interlayer dielectric film and thereafter polishing the conductive material, forming a lower electrode including a first conductive film containing a metal having at least one metal selected from a group consisting of Ir, Pt, Ru, Re, Ni, Co and Mo, silicon and nitrogen to be in contact with the plug, forming a first insulator film including an oxide dielectric film on the lower electrode and forming an upper electrode including a second conductor film containing the metal having at least one metal selected from the group consisting of Ir, Pt, Ru, Re, Ni, Co and Mo, silicon and nitrogen on the first insulator film.
In the method of manufacturing a dielectric element according to the second aspect, a dielectric element having excellent characteristics with the characteristics of the oxide dielectric film suppressed from deterioration resulting from hydrogen can be prepared due to the aforementioned structure.
In the method of manufacturing a dielectric element according to the aforementioned second aspect, the first insulator film including the oxide dielectric film is preferably patterned by light exposure. According to this structure, the dielectric element can be formed with no damage resulting from etching or the like when the oxide dielectric film is patterned.
In the method of manufacturing a dielectric element according to the aforementioned second aspect, the step of forming the first insulator film preferably includes a step of forming the first insulator film including the oxide dielectric film to cover the upper surface and the side surface of the lower electrode, and the step of forming the upper electrode preferably includes a step of forming the upper electrode to cover the upper surface and the side surface of the first insulator film. According to this structure, the side surface of the first insulator film including the oxide dielectric film is not exposed sideward, whereby hydrogen can be prevented from directly infiltrating into the oxide dielectric film and the interfaces between the oxide dielectric film and the lower and upper electrodes.
In the method of manufacturing a dielectric element according to the aforementioned second aspect, the plug preferably includes either a polysilicon plug or a tungsten plug. According to this structure, a generally employed technique of forming a polysilicon plug or a tungsten plug can be applied as such.
In the method of manufacturing a dielectric element according to the aforementioned second aspect, the lower electrode may include the first conductor film consisting of an IrSiN film and a Pt film formed on the first conductor film. The upper electrode may include the second conductor film consisting of an IrSiN film and a Pt film formed on the second conductor film. Further, the upper electrode may include a Pt film and the second conductor film, formed on the Pt film, consisting of an IrSiN film. In addition, the first insulator film including the oxide dielectric film may include an SBT film.
In the method of manufacturing a dielectric element according to the aforementioned second aspect, the first insulator film including the oxide dielectric film is preferably enclosed with the lower electrode including the first conductor film, the upper electrode including the second conductor film and a second insulator film having low permeability for hydrogen. According to this structure, an end of the oxide dielectric film not covered with the first and second conductor films is also enclosed with the second insulator film having low permeability for hydrogen, whereby hydrogen can be further suppressed from diffusing into the oxide dielectric film. In this case, the second insulator film having low permeability for hydrogen is preferably removed in a region other than an element region formed with the first insulator film, the lower electrode and the upper electrode. According to this structure, hydrogen can be suppressed from infiltrating into the element region including the oxide dielectric film while a step of recovering a MOS transistor with hydrogen can be unlimitedly carried out in the region other than the aforementioned element region.
In the structure of the aforementioned method of manufacturing a dielectric element, the second insulator film having low permeability for hydrogen preferably includes at least any of a silicon nitride film, a silicon oxynitride film and an aluminum oxide film. According to this structure, hydrogen can be effectively suppressed from infiltrating into the oxide dielectric film.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.